For several applications, real-time measurements of specific materials are necessary for safe and proper operations and experimentation. For example, neutron radiation experiments have conventionally used in-pile instrumentation to monitor and measure in-situ major physical parameters. Some of the most typical in-pile measurements include fuel or material sample temperatures, fuel rod or material sample dimensions, fission gas release in fuel rods, neutron flux, and gamma heating. In the case of measuring fuel rod or material sample dimensions, conventional elongation sensors and diameter gauges have been employed, including Linear Variable Differential Transformers (LVDTs) for measuring elongation and contraction of fuel rods or material samples.
Limitations in conventional instrumentation have arisen as the need for very precise real-time in-pile measurements has increased. For example, conventional LVDTs are typically limited in their ability to function in high temperature environments. Some LVDTs are available that are capable of functioning in environments of less than about 550° C. However, changes in length of materials and fuels being irradiated at temperatures greater than about 550° C. are not typically measurable in real time. To overcome the temperature limitations of conventional LVDTs, samples irradiated at higher temperatures are typically measured prior to and after irradiations. Such methods are very expensive and provide no real-time information of what is occurring during the irradiation. Additionally, errors are often introduced when samples are removed from the reactor.